Rotary actuators are used in many applications for providing rotational motion to devices. A particular application requiring high torque and positive braking action is in the driving of robot joints. Devices currently used to drive robot joints allow joint motion when unpowered. As a result, the devices require the addition of a separate braking device, or a position control system which remains continuously active to maintain the joint in a desired position. Both solutions, however, require additional hardware and control circuitry that add to the size, weight and cost of the systems.
Magnetostrictive motors employ magnetostrictive elements as the moving element. When magnetostrictive materials are subjected to a magnetic field directed along the principal orientation axis of the magnetostrictive material, the material expands in the direction of the field lines. Incompressibility of the material requires that it compress in orthogonal directions. This behavior has been used in magnetostrictive linear actuators. Such linear actuators, however, cannot provide rotational motion without gearing or other linear to rotational translational devices that add to the complexity, cost and size of the actuators.